Step 1: Recall the facts
Benzene is a toxic liquid and a known carcinogen. Long exposure damages bone marrow and can cause leukaemia.
Step 2: Others
Simple alkanes, alkenes and alkynes are not classed as carcinogens in this sense. So option (C).
Final Answer:
Benzene is carcinogenic and toxic, option (C).
\[ \boxed{\text{(C)}} \]